Synaptic proteins promote calcium-triggered fast transition from point contact to full fusion
Jiajie Diao,
Patricia Grob,
Daniel J Cipriano,
Minjoung Kyoung,
Yunxiang Zhang,
Sachi Shah,
Amie Nguyen,
Mark Padolina,
Ankita Srivastava,
Marija Vrljic,
Ankita Shah,
Eva Nogales,
Steven Chu,
Axel T Brunger
Affiliations
Jiajie Diao
Departments of Molecular and Cellular Physiology, Neurology and Neurological Sciences, Structural Biology, Photon Science and Howard Hughes Medical Institute, Stanford University, Stanford, USA
Patricia Grob
Department of Molecular and Cell Biology and Howard Hughes Medical Institute, University of California at Berkeley, Berkeley, USA
Daniel J Cipriano
Departments of Molecular and Cellular Physiology, Neurology and Neurological Sciences, Structural Biology, Photon Science and Howard Hughes Medical Institute, Stanford University, Stanford, USA
Minjoung Kyoung
Departments of Molecular and Cellular Physiology, Neurology and Neurological Sciences, Structural Biology, Photon Science and Howard Hughes Medical Institute, Stanford University, Stanford, USA
Yunxiang Zhang
Departments of Molecular and Cellular Physiology, Neurology and Neurological Sciences, Structural Biology, Photon Science and Howard Hughes Medical Institute, Stanford University, Stanford, USA
Sachi Shah
Departments of Molecular and Cellular Physiology, Neurology and Neurological Sciences, Structural Biology, Photon Science and Howard Hughes Medical Institute, Stanford University, Stanford, USA
Amie Nguyen
Departments of Molecular and Cellular Physiology, Neurology and Neurological Sciences, Structural Biology, Photon Science and Howard Hughes Medical Institute, Stanford University, Stanford, USA
Mark Padolina
Departments of Molecular and Cellular Physiology, Neurology and Neurological Sciences, Structural Biology, Photon Science and Howard Hughes Medical Institute, Stanford University, Stanford, USA
Ankita Srivastava
Departments of Molecular and Cellular Physiology, Neurology and Neurological Sciences, Structural Biology, Photon Science and Howard Hughes Medical Institute, Stanford University, Stanford, USA
Marija Vrljic
Departments of Molecular and Cellular Physiology, Neurology and Neurological Sciences, Structural Biology, Photon Science and Howard Hughes Medical Institute, Stanford University, Stanford, USA
Ankita Shah
Departments of Molecular and Cellular Physiology, Neurology and Neurological Sciences, Structural Biology, Photon Science and Howard Hughes Medical Institute, Stanford University, Stanford, USA
Eva Nogales
Department of Molecular and Cell Biology and Howard Hughes Medical Institute, University of California at Berkeley, Berkeley, USA; Life Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, USA
Steven Chu
Formerly Lawrence Berkeley National Laboratory, and Departments of Physics and Molecular and Cell Biology, University of California at Berkeley, Berkeley, USA
Axel T Brunger
Departments of Molecular and Cellular Physiology, Neurology and Neurological Sciences, Structural Biology, Photon Science and Howard Hughes Medical Institute, Stanford University, Stanford, USA
The molecular underpinnings of synaptic vesicle fusion for fast neurotransmitter release are still unclear. Here, we used a single vesicle–vesicle system with reconstituted SNARE and synaptotagmin-1 proteoliposomes to decipher the temporal sequence of membrane states upon Ca2+-injection at 250–500 μM on a 100-ms timescale. Furthermore, detailed membrane morphologies were imaged with cryo-electron microscopy before and after Ca2+-injection. We discovered a heterogeneous network of immediate and delayed fusion pathways. Remarkably, all instances of Ca2+-triggered immediate fusion started from a membrane–membrane point-contact and proceeded to complete fusion without discernible hemifusion intermediates. In contrast, pathways that involved a stable hemifusion diaphragm only resulted in fusion after many seconds, if at all. When complexin was included, the Ca2+-triggered fusion network shifted towards the immediate pathway, effectively synchronizing fusion, especially at lower Ca2+-concentration. Synaptic proteins may have evolved to select this immediate pathway out of a heterogeneous network of possible membrane fusion pathways.
